<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #yeye{
            width: 350px;
            height: 750px;
            border: 1px solid black;
            margin-top: 50px;
            margin-left: 50px;
            position: relative;
        }
        #father{
            width: 300px;
            height: 700px;
            border:1px solid red;
            margin-top: 50px;
            margin-left: 50px;
            /* 父相 子绝 */
            position:relative;
        }
        .s1{
            width: 300px;
            height: 100px;
            background-color: pink;
            /* 不占文档流 */
             position: absolute;
            top:0px;
            left: 0px; 

            z-index: 1;
            opacity:0.1;

        }
        .s2{
            width: 300px;
            height: 200px;
            float: left;
            background-color: blue;
        }
        .s3{
            width: 300px;
            height: 300px;
            background-color: yellow;

        }
    </style>
</head>
<body>
    <div id="yeye">
        <div id="father">
            <div class="s1">div1</div>
            <div class="s2">div2</div>
            <div class="s3">div3</div>
        </div>
    </div>
   
</body>
</html>